Identification of hormone-producing cells of the endocrine pancreas of the sea bass, Dicentrarchus labrax, by ultrastructural immunocytochemistry.

The hormone-producing cells of the endocrine pancreas of the sea bass Dicentrarchus labrax have been identified by ultrastructural immunocytochemistry. The glucagon cells have "clear" cytoplasm and contain characteristic electron-dense polygonal granules surrounded by a "halo" of electron-lucent material. The insulin cells have numerous, tightly packed, electron-dense granules that are almost twice as large as the peripherally located granules of the somatostatin cells. The pancreatic polypeptide cells have granules with variable electron density. When specific antisera are applied in the peroxidase-anti-per-oxidase immunocytochemical method at the electron microscope level, each of the four types of granule is identified by the resultant overlying immunoreaction deposit. Especially in older fish, a fifth, nonclassified type of cell has been identified within the endocrine pancreatic tissue. These cells have many ramifying processes and contain a mixture of the granules of the four endocrine cell types as well as granules from the exocrine tissue. It is suggested that these cells may be undertaking macrophage activities. A distinct patterned arrangement of the endocrine cell types in both small pancreatic islets and Brockmann bodies is observed. There is a central core of insulin and somatostatin cells surrounded by an outer peripheral layer of glucagon and pancreatic polypeptide cells. A definite functional interrelationship is suggested by this arrangement.